As silly I meant as imbalanced/improper not as whacky or awkward which are stamp of Divinity games
Healing from resistant element is not an original mechanic. In old RPGMaker 2003 games, the mechanic was beaten to death. For example attacking a shadow resistant creature with shadow spell caused you to heal the creature etc.
Soft caps on resistances along perks overriding that (for the case of Poison) would be a better approach in this case. Elementals can be given their own flags where they can be healed by their element.
Perhaps a perk for each element provided in an exclusive manner(if you get one, you can't take others) can be the way to go. You will spend a perk and choose only one element to heal you which would be a strategic decision.
